When an Editron inverter is used to generate an isolated AC microgrid (uGrid, uG), proper precautions and parameter settings are needed to allow protective devices such as fuses to work correctly in the grid installation in case of short-circuit or equipment malfunction.
Because the inverters cannot provide short-circuit current higher than the rated maximum current of the inverter, even "fast" fuses can be too slow to react to such currents, in comparison to the millisecond-level reaction of the inverters' internal overcurrent protection. To alleviate this, the inverters provide an overcurrent limitation, also known as voltage reduction function, which works by reducing the microgrid voltage (and optionally frequency) as a function of the output current. By doing so, the inverter can maintain a safe, but high enough current to burn normal AC fuses, while preventing the internal overcurrent protection from tripping the inverter completely.
The voltage reduction function is configured with the following parameters:
| Parameter | Unit | Function | Recommended value |
|
[FW 11] Voltage reduction, begin [FW 7] i_volt_reduction_begin |
A | Voltage of the microgrid will begin to reduce when output current is higher than configured value. |
Depends on inverter power rating and system components. Recommended 0.7 - 0.9 times the inverter rated current. Must be set lower than Voltage reduction, full. |
|
[FW 11] Voltage reduction, full [FW 7] i_volt_reduction_full |
A | Voltage of the microgrid will be fully reduced when current is higher than set value. |
Depends on inverter power rating and system components. Recommended 0.8 - 1.0 times the inverter rated current. Must be set higher than Voltage reduction, begin. |
|
[FW 11] Max voltage reduction [FW 7] volt_reduction_coef_full |
- | Coefficient of fully reduced microgrid voltage. A value of 0.7 will result in the microgrid voltage being 0.7 times the nominal voltage when output current is higher than the full voltage reduction limit. |
Depends on the installed fuse size, grid impedance, and other system properties. Recommended 0.1 - 0.7 |
|
[FW 7 only, deprecated] time_filt_volt_reduction_coef_down |
s | Filter time of decreasing voltage coefficient (filter time used when microgrid voltage is reducing due to high current). | Should be always set to 0. |
|
[FW 11] Removing voltage reduction filter time [FW 7] time_filt_volt_reduction_coef_up |
s | Filter time of increasing voltage coefficient (filter time used when microgrid voltage is returning back to nominal). |
Can be adjusted according to system properties. Recommended 0.5 - 3 |
|
[FW 11] Enable frequency reduction [FW 7] frequency_reduction_ena |
- | Enable or disable reduction of frequency. If enabled, frequency will be reduced such that V/f remains constant. | Enabled or disabled according to system properties. |
The voltage reduction function is always enabled, but it can be effectively disabled by setting the current limits higher than the inverter rated current, or setting the reduction coefficient to 1.